Surgical cast and process of forming it



United States Patent SURGICAL CAST AND PROCESS OF FORMING IT Ernest A.Rodman, Newburgh, N. Y., assignor to E. I. du Pont de Nemours andCompany, Wilmington, Del., a corporation of Delaware No Drawing.Application July 19, 1952, Serial No. 299,903

4 Claims. (Cl. 128-90) This invention relates to stilfening bandages andtheir manufacture.

Calcined gypsum, commonly known as plaster of Paris (CaSO4- /2H2O), iswidely used for surgical casts for holding broken bones in alignmentwhile the injured member is healing. The plaster of Paris type of casthas many inherent disadvantages, such as heavy weight, being messy toapply and, in the case of hospitals, requiring a separate room forapplying.

An object of this invention is to provide an improvement in surgicalcasts. A further object is the provision of a lightweight surgical castwhich may be readily applied to an injured body member. A still furtherobject is the provision of a coated fabric stiffening bandage which maybe quickly softened by wetting with water and may be so treated that itwill dry to a stiff non-water soluble bandage, and process of makingsame. A still further object is the provision of a coated fabricstiffening bandage which will not adhere to a persons skin but will becohesive when wound upon itself. These and other important objects willbe readily apparent to those skilled in the art, as the description ofthe invention proceeds.

The foregoing objects are accomplished by impregnating and/or coating afabric with an aqueous solution of a water-soluble Group I alkali metalsalt of an acidic copolymer of vinyl acetate and crotonic acid andsufiicient inert filler to impart stiffness to the coated fabric whendry and allowing the coating to dry to a relatively stiff condition butyet remain sufficiently pliable so it can be wound upon itself. The dryrelatively stiff coated fabric is rendered supple and cohesive bywetting with water so that the superposed plies, when wrapped around aninjured body member, will adhere and form a rigid bandage when dry.After it is in place it is treated with an aqueous solution of apolyvalent metal salt to make the coating water-insoluble when dry.

The following specific examples are given as illustrations and not aslimitations. Throughout the specification and appended claims the partsand percentage figures are expressed on a weight bas1s.

Example 1 Per cent Copolymer of 95 parts vinyl acetate and 5 partscrotonic acid Sodium bicarbonate :8 China clay 16.7 Water 74.3

The above composition was agitated until homogeneous, forming thewater-soluble sodium salt of the acidic copolymer resin in situ. Acotton gauze fabric running 10.4 yards per pound per 36" wldth,similanto that employed for surgical bandages, was dipped into the abovecomposition and the excess allowed to drain off, after which the treatedfabric was passed through a heat zone to evaporate the water and dry thecoating.

Example I] A White stiffening bandage material was prepared in the samemanner as described in Example I, except the cotton gauze was treatedwith the following composition:

2,697,434 Patented Dec. 21, 1954 Per cent Copolymer of partsvinyl-acetate and 5 parts crotonic a id Example III A stiif bandagematerial was prepared by dip coating a polyacrylonitrile fabric weighing2.8 ounces per square yard and having a thread count of 52 x 25, withthe composition of, and in the same manner as, Example H.

Example IV A stiff bandage material was prepared by dip coating apolyethylene terephthalate fabric with the composition of, and in thesame manner as, Example 11.

The impregnated and/or coated fabric bandage materials described in thepreceding examples are all dried immediately following the dip coatingand are relatively stiff but sufiiciently flexible to be rolled on a oneinch diameter tube. The treated fabrics may be stored indefinitely atthis stage. When the bandage is to be applied to a body member it isimmersed in water for a few seconds which makes it limp and cohesive butnot adhesive. It does not adhere to human skin. The waterwet bandagereadily conforms to body contours when it is wrapped around a bodymember four to six times. After the water-wet bandage has been wrappedaround a body member, and while it is still wet, it may be treated withan aqueous solution of a polyvalent metal salt, such as the polyvalentmetal alums, magnesium sulfate or calcium oxide, to render the coatingwater-insoluble by the in situ formation of the water-insoluble salt ofthe polyvalent metal and the copolymer. Both aluminum and iron alumsfunction properly, but aluminum alums are preferred since they do notdiscolor the bandage. The wet coating is cohesive and the severalconvolutions become laminated on air drying of the bandage. The amountof polyvalent metal salt required may vary but must be sufficient torender the resin binder water-insensitive.

The dry material of Examples III and IV when wetted with water becamelimp and cohesive and, when wound around a finger with six convolutions,stuck together and set up to a rigid bandage in about 5 minutes, andbecame essentially dry in 10 minutes with air drying. This is less timethan is required for bandages made on a cotton gauze fabric, and isprobably due to less water being absorbed by the fabric.

The bandage may be wetted by steam to render it supple and cohesive, inwhich case a minimum of excess watler is absorbed and the drying time isreduced accordmg y.

Where a water-insoluble bandage is not required the polyvalent metalsalt treatment may be eliminated.

In the specific examples the acidic copolymer resin is renderedwater-soluble by forming, in situ, the sodium salt of the copolymer inan aqueous medium. Other Group I monovalent alkali metal salts of thecopolymer, such as the lithium, potassium, rubidium and caseium salts,may also be employed.

The water-soluble hydroxides, carbonates and bicarbonates of the Group Ialkali metals may be used to form the water-soluble salt in situ. About5 to 10 parts of the Group I monovalent alkali metal salt or hydroxideare preferred for each parts of the acidic copolymer resin, although aslittle as 3 parts per 100 parts of resin may be used. The amount ofGroup I monovalent alkali metal salt or hydroxide required is theequivalent amount of alkali metal necessary to react with the acidgroups present to produce essentially a neutral coating. When using thehydroxides, the amount must be sufficient to maintain the pH below about7.5.

The acidic copolymer resin derived from 95 parts earth. The morereactive'fillers,'such as calcium carbonate; calcium sulfate andmagnesium oxide, while useful, arenot'preferred-sincethecoating'is'less'cohesive than when completelyinertfillers are used. In place of titanium dioxideotherpigmentsy'suchas-zinc*oxide, an-

timony oxide, zinc sulfide, or colored pigments, may be used, as long asthey are inert with respect to the copolymer resin. Theminir'n'urnamount of loading of the coating with fillers and/or pigments:to obtain the necessary stiffness is one-half p'art for each-partof'thc copolymer resin. When the amount of filler and pigment isincreased beyond 3 parts'forxeach-part of copolymer resin the cohesiveproperty deteriorates to an undesirable extent.

In the claims the term inert filler is used to designate pigments andcolorless fillers which are inert with respect to the copolymer resin.

The amount of coating on the fabric is not critical and may vary over awide range. Satisfactory results have been obtained with 1.0to 6.0ounces of dry coating per square yard, depending on the type andconstruction of fabric. However, if more than 7 ounces of coating persquare yard are employed there is no additional advantage in stiffnessand there are disadvantages of longer drying and a greater tendency forthe dry coating to powder off in handling the bandage material beforewetting. If the fabric is an open weave fabric and not very absorbent,less coating will be required thanif the fabric is closely woven andconsists of absorbent fibers. 111 some cases the interstices may becompletely filled, whereas in others they may remain open to permit easypassage of moisture during the drying of the bandage.

The type or construction of the supporting fabric is not critical, but alightweight openweave fabric, similar to a leno weave, is preferred;Cotton fabrics are preferred for economic reasons, although fabrics madefrom synthetic fibers such as, e. g. polyacrylonitrile, polyethyleneterephthalate, 'nylon, polyvinyl chloride and various copolymersthereof, and various cellulose derivatives, are satisfactory. Thesynthetic fibers which do not absorb water or are not softened by waterdry faster than cotton fabric after the bandage has been wetted and putin place. Non-woven fabrics, such as those disclosed in co'pendingapplication S. N. 232,245, filed June 18, 1951, by]. A. Picc'ard may-beused in place of the woven fabricsdisclosed in the examples. Certainpapers may also be used.

Throu hout the specification 'an'dclaims impregnating and coatingare'usedsynonymously. In the case of coatings applied to gauze fabrics"with wide interstices there is no fundamental diife'rencebetweenimpregnation and coating. It is also immaterial whether the coatingcomposition is applied'directly to one orboth sides of the fabric orwhether the fabric is completely immersed in the coating. Usefulproducts canbe made by coating only one side even where the fabric is sotightly woven that the coating does not strike through the fabric.

The products of this invention are particularly useful for stiffeningbandages to replace plaster casts on injured body members. It will bereadily apparent to those skilled in the art that the products of thisinvention have other uses, where the coated fabric is used as a singleply. The process herein described, in which a water-insoluble resin isconverted to a water-soluble salt in an aqueous medium and then appliedto a fabric substrate, after which it is rendered water-insoluble by thein situ formation of a'polyvalent metal salt, provides an economicadvantage by avoiding costly organic solvents and their recovery.Fabrics coated with the waterinsoluble polyvalent metal salt of thecopolymer, properly pigmented, areuseful as case coverings,bookbindings, window shades, luggage linings, etc.

It is apparent that many widely different embodiments of this inventionmaybe made without departing from the spirit and scope thereof and,therefore, it is not intended to be-limited except'as indicatedin theappended claims.

I claim:

1.- A surgical cast comprising a plurality 'of convolutions, cohesivelyunited, of a fabric having a coating of a water-insoluble salt of apolyvalent metal and a copolymer resin of -98 parts of vinyl acetate andl02-parts of crotonic acid, and 0.5 to 3 parts of inert filler per partof copolymer resin.

2. A surgical cast comprising a plurality of convolutions, cohesivelyunited, of a fabric having a coating of a water-insoluble magnesium saltof an acidic copolymer 'resin of '90-'98 parts vinyl acetate and l02parts crotonic acid and 0.5 to 3 parts of inert filler-per part ofcopolymer resin.

3. Process of preparing a surgical cast materialwhich comprises coating21 flexible fabric with an aqueous coating comprisinga water-solubleGroup I alkali metal salt ofan acidic copolymer resin of90-98 partsvinyl acetate and 10-2 parts crotonic acidand 0.5 to 3- parts ofine'rtfillerjper each part of copolymer resin, dr'ying thecoated-fabric, immersing the dry -coated fabric in water tosoftenand'-'activate the cohesive property of the' salt, wrapping aplurality of convolutions around a member to be bandaged, converting[the water-soluble coating to a water-insoluble coating by treating thewet bandage withan aqueous solution of a p olyvalent metal compound, andallowing the waterto evaporate.

4. 'Thepr'ocess of claim 3 in which'the copolymer resin comprisesparts"vin'yl acetate-and 5' parts crotonic acid.

References Cite d in the file of thispatent UNITED STAT-'13s PATENTSNumber I, Name Date 2,263,598 Stark et'al. Nov. 25, 1941 "2,616,418Eberl NOV. 4, 1952 i OTHER "REFERENCES Ser. No. 337,664, Heather 51;AFP. C.),pi1b lished May 11, 1943.

1. A SURGICAL CAST COMPRISING A PLURALITY OF CONVOLUTIONS, COHESIVELYUNITED, OF A FABRIC HAVING A COATING OF A WATER-INSOLUBLE SALT OF APOLYVALENT METAL AND A COPOLYMER RESIN OF 90-98 PARTS OF VINYL ACETATEAND 10-2 PARTS OF CROTONIC ACID, AND 0.5 TO 3 PARTS OF INERT FILLER PERPART OF COPOLYMER RESIN.